Motohiko Murakami

Motohiko Murakami was awarded the 2013 James B. Macelwane Medal at the AGU Fall Meeting Honors Ceremony, held on 11 December 2013 in San Francisco, Calif. The medal is for “significant contributions to the geophysical sciences by an outstanding early career scientist.”

Citation

The James B. Macelwane Medal of AGU is presented to Motohiko Murakami for his discovery of the postperovskite phase of MgSiO3, for a new class of sound velocity measurements under lower mantle pressure-temperature conditions that have changed our view of whole-Earth chemistry, and for other fundamental contributions that have furthered our understanding of the Earth’s deep interior.

As part of his Ph.D. research, Dr. Murakami discovered that MgSiO3-perovskite, the most abundant component of the lower mantle, transforms to a “postperovskite” phase under P-T conditions corresponding to the D” seismic zone, just above the core-mantle boundary. This work, published in a 2004 Science paper, instantly provided an explanation for anomalous seismic features in D”, including the D” seismic discontinuity. Equally important, the phase relations of postperovskite give us an absolute temperature above the core-mantle boundary. This is the only measured anchor point for the lowermost mantle geotherm. Murakami’s pioneering work with his advisor Kei Hirose triggered an instantaneous flood of theoretical and experimental research in laboratories worldwide, quickly confirming his discovery. Murakami followed this up with experiments to establish the stability of postperovskite for a more realistic mantle composition and the partitioning of Fe among coexisting phases. His results have stimulated a new generation of models for the dynamics and chemistry of the lowermost mantle and for the heat flux across the core-mantle boundary. It is hard to imagine a single contribution that could have exceeded the impact of the discovery of postperovskite for deep interior research; it is one of the most important discoveries of the past several decades in solid Earth geophysics.

Most recently, Murakami changed research directions to design and build a Brillouin spectrometer with laser heating on an X-ray beam line of the SPring-8 synchrotron. The aim was to measure acoustic velocities on minerals under actual lower mantle P-T conditions. Recent results on perovskite and ferropericlase give compelling, direct evidence that the lower mantle is perovskite and silica enriched compared with a lherzolite or “pyrolite” upper mantle. Thus, Earth’s mantle appears to be chemically stratified, but with a whole-mantle composition that is more compatible with cosmochemical models than previously thought. Murakami has been following up this groundbreaking work with similar measurements on other likely components of the lower mantle, such as calcium silicate perovskite and sodium silicate high-pressure phases.

The seminal contributions of Motohiko Murakami have had profound implications for mineral physics, seismology, geodynamics, and geochemistry. The earmark of Murakami’s research is to tackle the most important problems he can think of, even if it takes years to build equipment needed for experiments and entirely new skill sets. Although this is an excellent game plan, it is a risky one that takes dedication, focus, and an unusual amount of sheer skill for success. Motohiko has these qualities and has produced a body of work of exceptional impact that cuts across disciplinary boundaries. It is a pleasure to honor him with the 2013 Macelwane Medal of AGU.

—JAY BASS, Consortium for Materials Properties Research in Earth Sciences (COMPRES), Champaign, Ill., and University of Illinois at Urbana-Champaign

Response

Thank you very much, Jay, for your generous citation and for all of your support. It is a great honor for me to receive this medal. First, I sincerely thank AGU for this recognition and my nominators for their support and time.

I would certainly not be standing here today if I had not met many teachers, mentors, colleagues, and friends who have always helped and encouraged me along the way, and I really appreciate this great opportunity to express my gratitude to them.

As a student, I was very fortunate to work under the guidance of two great mentors, Shigenori Maruyama, my undergraduate advisor, and Kei Hirose, my Ph.D. advisor, at Tokyo Institute of Technology, who strongly inspired and encouraged my research interest in the deep Earth’s interior. I learned a lot from Maruyama-sensei and Kei concerning their enthusiasm and attitude toward science. I would also like to thank my young and brilliant colleagues at Tokyo Institute of Technology for their energy and passion for pushing Earth science forward.

After my Ph.D., I had the great luck to work with Jay Bass at the University of Illinois. Jay has always been exceptionally generous with his support, time, and knowledge, and I learned so much from Jay on the special experimental techniques for sound wave velocity measurements under high pressure through a collaboration with Stas Sinogeikin, who is a master of all those tricks. Through Jay, I was also given the tremendous opportunity to interact with many excellent young people, including Carmen Sanchez-Valle, Dmitry Lakshtanov, and Jennifer Jackson.

At the Institute for Study of the Earth’s Interior, Okayama University, I had the privilege to join the group of many talented scientists in high-pressure mineral physics led by Eiji Ito, a great master of high-pressure experiments. I have particularly enjoyed interacting with Ito-sensei, Tomoo Katsura, Masami Kanzaki, Akira Yoneda, and Xianyu Xue and have also learned a great deal from amazing young scientists such as Daisuke Yamazaki and Takashi Yoshino. Thank you for your energy and enthusiasm.

I have been working at Tohoku University for almost 6 years now, with many talented scientists and young brilliant students. My special thanks go to Eiji Ohtani for his guidance and continuous encouragement throughout my academic carrier. It has been my great privilege to closely work with Ohtani-sensei.

Over the last few years, I have had the wonderful opportunity to meet a number of outstanding mentors and scientists who have influenced and taught me much such as Shun-ichiro Karato, Guillaume Fiquet, Alex Goncharov, Jan Matas, John Hernlund, Naohisa Hirao, Yasuo Ohishi, Shinji Kohara, and John Sandercock. I am so grateful to them all for their guidance, mentorship, and enthusiasm.

Most important, I thank my wife, Michiyo, for her patience and encouragement and our two wonderful kids, Setoka and Haru­hiko, for giving me an invaluable perspective on life. Finally, I want to thank my parents, Katsuhiko and Yumiko, whose support made it possible for me to become an Earth scientist.